LAG3 (CD223) is a cell surface molecule expressed on activated T cells (Huard et al. Immunogenetics 39:213-217, 1994), NK cells (Triebel et al. J Exp Med 171:1393-1405, 1990), B cells (Kisielow et al. Eur J Immunol 35:2081-2088, 2005), and plasmacytoid dendritic cells (Workman et al. J Immunol 182:1885-1891, 2009) that plays an important role in the function of these lymphocyte subsets. In addition, the interaction between LAG3 and its major ligand, Class II MHC, is thought to play a role in modulating dendritic cell function (Andreae et al. J Immunol 168:3874-3880, 2002). Recent preclinical studies have documented a role for LAG-3 in CD8 T-cell exhaustion (Blackburn et al. Nat Immunol 10:29-37, 2009).
As with chronic viral infection, tumor antigen-specific CD4+ and CD8+ T cells display impaired effector function and an exhausted phenotype characterized by decreased production of pro-inflammatory cytokines and hyporesponsiveness to antigenic re-stimulation. This is mediated by cell extrinsic mechanisms, such as regulatory T-cells (Treg), and cell intrinsic mechanisms, such as inhibitory molecules that are upregulated on exhausted, tumor-infiltrating lymphocytes (TIL). These inhibitory mechanisms represent a formidable barrier to effective antitumor immunity.
LAG—is expressed on tolerized TILs suggesting that they contribute to tumor-mediated immune suppression. Inhibition of LAG3 may lead to enhanced activation of antigen-specific T cells from which a therapeutic benefit may be gained. There is a need in the art for high efficacy therapeutic antibodies which antagonize the activity of LAG3 which can be used to generate a robust immune response to tumors.